Interpretive Summary: Egg parasitoids of the genus Trichogramma are important insect natural enemies worldwide. This paper reviews the effect of habitat and various plant characteristics on parasitism by Trichogramma. A number of factors may affect parasitism rates including plant spacing, plant structure, surface structure and chemistry, plant volatiles and plant color. Plants can also affect parasitoids by food for adults and via the nutritional quality of the host eggs. Understanding the impacts of the host plant can have important implications for biological control and for assessing risks to non-target organisms.

Technical Abstract:
Egg parasitoids of the genus Trichogramma are among the most important natural enemies worldwide. Parasitism levels by Trichogramma vary greatly among different habitats, plants or plant structures on which the host eggs are located. Here we summarise the published evidence on mechanisms that may underlie the observed variation in parasitism rates. These mechanisms include plant spacing, plant structure, plant surface structure and chemistry, plant volatiles and plant color. In addition, plants can affect parasitoid behaviour and activity by providing carbohydrate food sources such as nectar to the adult wasps, and by affecting the nutritional quality of the host eggs for progeny development. Knowledge of plant and habitat factors that affect Trichogramma spp. efficacy has important implications for biological control, and for assessing the risks that mass released Trichogramma spp. may pose to non-target insects.